This application claims the priority of German Patent Application No. 198 13 053.8, filed Mar. 25, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention is directed to a reactor unit.
Reactor units for catalytic chemical conversion of a gaseous or liquid reaction starting product into a reaction end product that contains a gaseous or liquid reaction component, which is selectively separable by membrane diffusion, are used, for example, for steam reforming of methanol. In steam reformation of methanol, the reaction end product is a hydrogen-rich mixture containing a certain proportion of carbon monoxide. The use of such reactor units in mobile applications (e.g., in fuel cell powered motor vehicles) in order to obtain the hydrogen required for the fuel cells from liquid methanol carried on board is known.
Since carbon monoxide has a harmful influence on the fuel cells, the reaction end product requires suitable chemical treatment. One known possibility is the selective separation of the hydrogen by membrane diffusion. For mobile applications, particularly automotive engineering, it is desirable for reasons of space and dynamics for the reactor to be compact and easy to construct with as few components as possible, thereby minimizing regulation and control units and at the same time aiming for high efficiency.
U.S. Pat. No. 4,981,676 discloses a reactor unit for steam reforming of a hydrocarbon, in particular methane, containing a tubular reaction chamber filled with a suitable catalyst pellet charge. The reaction chamber is delimited externally by a metal wall that is externally heatable by a burner supplied with a fuel/air-gas mixture, which is burned in an open flame. The heat generated by the burner can be used to heat the system rapidly or to maintain a suitable elevated reaction temperature in the case of endothermic chemical reactions. On the inside, the reaction chamber is composed of a tube acting as a hydrogen separating membrane with a corresponding porous ceramic tube wall.
Reforming reactor units have been proposed in which, in addition to a hydrogen separating membrane, a burner designed to carry out catalytic combustion is integrated with the reaction chamber itself into a single unit. See, for example, German Patent Application 197 57 506; U.S. patent application Ser. No. 09/210,894 filed Dec. 16, 1998.
U.S. Pat. No. 5,451,386 discloses a reactor unit containing a membrane tube with a selectively hydrogen-permeable wall. The interior of the tube forms the reaction chamber, which contains suitable catalyst particles in order to obtain hydrogen by catalytic decomposition of ammonia or hydrogen sulfide, for example.
Membranes for separating a desired reaction component from a mixture of substances containing this component, particularly for separating hydrogen from a mixture containing hydrogen, are already used in various designs and consist of various materials. One known design is the monolithic block with several parallel lengthwise channels delimited by porous membrane walls that are selectively permeable for the desired reaction components. The mixture from which the desired reaction components are to be separated is conducted through the interior lengthwise channels. Membrane blocks of this type are used, for example, for filtration or separation purposes or used in catalytic chemical reactions. In catalytic chemical reactions, the catalyst material can be added to the block material. See EP 0 442 410 A1, U.S. Pat. No. 5,409,609, and German Patent 691 07 096 T2. German Patent 691 07 096 T2 teaches the use of the membrane device described therein as a reactor unit.
European patent document EP 0 450 872 A1, incorporated by reference herein in its entirety, describes a reactor unit for conducting an endothermic catalytic reaction of a gaseous or liquid reaction starting product into a reaction end product. The reactor unit contains a cylindrical reaction chamber traversed by one or more ceramic burner tubes extending in the lengthwise direction of the cylinder and at a distance from one another. A fuel inlet tube is inserted coaxially into each burner tube.
The object of the present invention is to provide a reactor unit that is relatively compact and easy to build, and has high conversion efficiency.
The reactor unit according to the present invention achieves this object. The reactor unit contains a monolithic block with several parallel lengthwise channels in the reaction chamber, into which the reaction starting product can flow and which contain a suitable reaction catalyst material. The channels are delimited externally by walls that are membranes for the selective separation of the desired reaction components from the reaction end product. At least some of these lengthwise channels each have their own catalytic burner (1) to generate, by a flameless catalytic combustion process, heat for rapid heating of the reaction chamber formed by the lengthwise channels; and/or (2) to maintain a sufficiently high reaction temperature to carry out the desired catalytic chemical reaction in the reaction chamber, particularly for an endothermic reaction.
Integration of both a separating membrane and a catalytic burner into a monolithic block that forms the reaction chamber with its lengthwise channels makes possible a particularly compact design of the reactor unit with a given efficiency. The block can be made low in weight and relatively inexpensively, for example, as an extruded profile. The compact design is favorable for rapid dynamic behavior of the reactor unit under varying load conditions, such as occur in mobile applications in motor vehicles. The reactor unit can thus be used in particular to obtain hydrogen by steam reforming of methanol in fuel cell powered motor vehicles.
In an embodiment of the present invention, each catalytic burner has a burner tube inside its reaction chamber lengthwise channel. The burner tube has a suitable burner catalyst material inside for catalytic combustion of a fuel fed into the interior of the burner tube. In a further embodiment of this reactor unit, the burner catalyst material is applied to the inside of the burner tube as a coating.
In another embodiment of the reactor unit according to the present invention, the block walls functioning as separating membranes are made of a porous carrier material provided with a separation-active coating. The separation-active coating contains one or more finely porous separation-selective plastic and/or ceramic layers and/or a metal layer made of a separation-selective metal material. The block walls so made have high selectivity for separation of the desired reaction components (e.g., hydrogen) from a reaction end product containing hydrogen.
In another embodiment according to the present invention, it collecting channels running transversely are formed in the block, through which channels the reaction components that diffuse selectively through the membrane walls of the block can be removed separately from the remaining components of the reaction end product.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.